Heat oil over medium heat. Add cumin seeds and let sizzle for 30-60 seconds until fragrant.
Add onion, ginger, and garlic. Cook 8–12 minutes, stirring often, until golden-brown. Deglaze with a splash of water if it sticks.
Add green chilies and cook 2–3 minutes.
Add tomatoes and salt. Cook 6–8 minutes until tomatoes soften and the mixture deepens in color.
Add turmeric, chili powder, coriander, and ground cumin. Cook 2-3 minutes, stirring, adding a splash of water if dry.
Stir in the homemade seitan and cook 2-3 minutes to coat with the masala. Pour in broth/water and bring to a gentle boil.
Stir in garam masala and lower heat. Then add soy milk and simmer for 4-6 minutes, then adjust thickness with more soy milk/broth or extra simmering.
Turn off heat, garnish with cilantro, and serve with rice or rotis.